Fix NPE. b/11882251

Change-Id: Ia15f9aa96f4141e7e7dc0b1d285c888b4aac683a
diff --git a/src/com/android/mail/print/PrintUtils.java b/src/com/android/mail/print/PrintUtils.java
index 530e73e..0e180c7 100644
--- a/src/com/android/mail/print/PrintUtils.java
+++ b/src/com/android/mail/print/PrintUtils.java
@@ -56,6 +56,9 @@
     public static void printConversation(Context context,
             MessageCursor cursor, Map<String, Address> addressCache,
             String baseUri, boolean useJavascript) {
+        if (cursor == null) {
+            return;
+        }
         final String convHtml = buildConversationHtml(context, cursor,
                         addressCache, useJavascript);
         printHtml(context, convHtml, baseUri, cursor.getConversation().subject, useJavascript);